1. Field of the Invention
The present invention relates to a cylindrical grinder and a cylindrical grinding method which can perform traverse grinding on an outer circumference of an ingot of silicon single crystal.
Priority is claimed on Japanese Patent Application No. 2009-042888, filed Feb. 25, 2009, the contents of which are incorporated herein by reference.
2. Description of Related Art
Previously, a wafer used in a semiconductor device has been manufactured by producing an ingot of silicon single crystal (crystal rod) by a Czochralski method (CZ method), traverse grinding an outer circumference of the ingot by a cylindrical grinder to finish the ingot to have a predetermined dimension (diameter), and slicing the ingot in a direction perpendicular to an axis line of the ingot.
For example, FIG. 18 shows one example of a cylindrical grinder A of a related art which traverse grinds the outer circumference of an ingot 1. The cylindrical grinder A includes a support unit 2 clamping the ingot 1 at both sides thereof in a direction of axis line O1 in a state in which the direction of the axis line O1 is disposed along a horizontal direction (a transverse direction T1) and clampingly holding the ingot 1 to rotate the ingot 1 around the axis line O1, and a grinding unit 3 disposed so as to be able to move in the direction of the axis line O1 of the ingot 1 (a horizontal direction, a transverse direction T1) grinding the outer circumference of the ingot 1 while moving in the direction of axis line O1. Such a related art is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2008-200816, Japanese Unexamined Patent Application Publication No. 2001-259975, and Japanese Unexamined Patent Application Publication No. Hei 11-291145.
The support unit 2 includes a pair of left and right support devices 4 and 5 for holding both end portions 1a and 1b side of the ingot 1 in a direction of axis line O1. The support device 4 has a main shaft (driving shaft) 4a rotating around a central axis line O2, for example, by driving of a motor or the like, and a holder 4b fixedly installed to a leading end portion of the main shaft 4a to hold one end portion 1a side of the ingot 1. The other support device 5 is installed to be freely rotated around a central axis line O3, and includes an auxiliary shaft (driven shaft) 5a installed to be moved in a direction of the central axis line O3, for example, by a hydraulic cylinder or the like, and a holder 5b, fixedly installed to a leading end of the auxiliary shaft 5a, for holding the other end portion 1b side of the ingot 1.
When the ingot 1 of silicon single crystal is traverse ground by using the cylindrical grinder A, firstly, the ingot 1 is set between the pair of left and right support devices 4 and 5 in a state in which the direction of axis line O1 is disposed along the transverse direction T1, and one end portion 1a side of the ingot 1 is mounted and held to the holder 4b of the one support device 4. In addition, the holder 5b is moved together with the auxiliary shaft 5a of the other support device 5 to be mounted on the other end 1b side of the ingot 1, so that the ingot 1 is clampingly held by the pair of left and right support devices 4 and 5.
When the main shaft 4a and the holder 4b of the one support device 4 are rotated, the ingot 1 is rotated around the axis line O1. The auxiliary shaft 5a and the holder 5b of the other support device 5 are rotatingly driven around the central axis line O3, so that the ingot 1 is rotated around the axis line O1, with the ingot 1 being clampingly held by the pair of left and right support devices 4 and 5.
A rotating grind stone 3a of the grinding unit 3 is pressed against the outer circumference of the ingot 1 which is rotated around the axis line O1, and the grinding unit 3 is moved in the transverse direction T1 along the direction of axis line O1 of the ingot 1 to sequentially grind the outer circumference of the ingot 1 and thus finish the ingot 1 to have a predetermined dimension (a diameter).
In order to manufacture more wafers from one ingot 1 and also manufacture a wafer of a large diameter such as a wafer of 450 mm in diameter, recently, the ingot 1 to be cylindrically ground has grown in size (increased in length and diameter) and in weight.
Since the cylindrical grinder A of the related art is adapted to clampingly hold the ingot 1 by using the support unit 2 (i.e., the pair of left and right support devices 4 and 5) in the state in which the direction of axis line O1 is disposed along the transverse direction T1, as shown in FIG. 19, there is a problem in that when the enlarged and weighted ingot 1 is cylindrically ground, deformation occurs in the ingot 1, and thus process precision is deteriorated.
Meanwhile, when the ingot 1 of silicon single crystal is produced, for example, by using the Czochralski method, a straight barrel portion 6 of a cylindrical rod shape is formed at a center portion in the direction of axis line O1, and a conical top portion 7 and a conical tail portion 8 are formed at both end portions 1a and 1b sides of the ingot 1 in the direction of axis line O1. For example, in the case in which it is necessary to cut a sample, when the ingot 1 is manufactured, there is a case in which a slip dislocation of the single crystal occurs in the tail portions 8. When generation of dislocation occurs in the tail portion 8, the top portion 7 or the tail portion 8 may be cut by using a band saw or the like prior to cylindrical grinding.
When the ingot 1 with the cut top portion 7 or the cut tail portion 8 is cylindrically ground, as shown in FIGS. 20 and 21, end faces 1c and 1d (1a and 1b) of the ingot 1 are clampingly held by the holders 4b and 5b of the pair of left and right support devices 4 and 5. In the cylindrical grinder A of the related art, since an acting direction of a clamping force F1 applied from the pair of left and right support devices 4 and 5 is perpendicular to an acting direction of the weight W1 of the ingot 1 itself and an acting direction of a process load W2 applied from the grinding unit 3, as the ingot 1 grows in size and in weight, slippage is likely to occur between the ingot 1 and the holders 4b and 5b of the support unit 2, so that positional deviation occurs in the ingot 1 to deteriorate the process precision.
Although it may be contemplated that strong clamping force F1 is applied to the ingot 1 to prevent the positional deviation of the ingot 1, a large-sized support unit 2 (the support devices 4 and 5) is necessary in this instance. In addition, in the case of cylindrically grinding the ingot 1 (dislocation occurring product) of which generation of dislocation occurs at the crystal of the tail portion 8, since compressive stress of the dislocation occurring crystal is weaker than that of the dislocation-free crystal, the ingot 1 may become damaged if the ingot 1 is held with the strong clamping force F1. For this reason, when the ingot 1 of the dislocation occurring product is ground by the cylindrical grinder A of the related art, it is necessary to cut the dislocation occurring portion of the tail portion 8 prior to the cylindrical grinding.
In addition, in the case where the ingot 1 is clampingly held in the state in which the direction of axis line O1 is disposed along the transverse direction T1, as shown in FIG. 18, while the ingot 1 is moved in a vertical direction T2 or a back and forth direction T3 (a transverse direction) in the state in which the direction of axis line O1 is disposed along the transverse direction T1, it is necessary to perform centering by coinciding the axis line O1 of the ingot 1 with the central axis lines O2 and O3 of the main shaft 4a and the auxiliary shaft 5a of the support devices 4 and 5 (i.e., placing them substantially coaxially). Further, when the ingot is clampingly held by the pair of left and right support devices 4 and 5, the axis line O1 of the ingot 1 may be deviated. In this instance, after the clampingly held state is released for a while, it is necessary to correct the centering by moving again the ingot 1 in the vertical direction T2 or back and forth direction T3. Therefore, in the cylindrical grinder A of the related art which clampingly holds the ingot 1 in the state in which the direction of axis line O1 is disposed along the transverse direction T1, there is a problem that a lot of manpower is required for the centering (or correction of the centering).
For example, as disclosed in Japanese Unexamined Patent Application Publication No. 2009-190142, a cylindrical grinding method has been known in which a cylindrical block formed by cutting an ingot to be short is vertically placed and then an outer circumference thereof is ground. However, this method requires a process of cutting and removing a top portion and a tail portion and cutting again the ingot in several blocks of a cylindrical shape. In addition, a long time is required when the ingot with the top portion and the tail portion removed is positioned, thereby deteriorating productivity.